David Foster Says He Will 'Never Disclose' Reason Why He and Yolanda Hadid Divorced

David Foster is keeping tight-lipped about what led to his divorce from Yolanda Hadid.

In the new Netflix documentary David Foster: Off the Record, which premiered on Wednesday, the Grammy winner, 70, opens up about both his professional and personal life, including his 2015 split from Hadid, his fourth wife.

At the time, Hadid was battling a Lyme disease diagnosis, however, Foster said her health was not the cause of their ending marriage.

"How can I leave a sick woman?" said Foster in the documentary. "The fact of the matter is that was not the reason I left. It was for a different reason — which I will never disclose — that had nothing to do with her being sick."

Foster, who recently celebrated his one-year wedding anniversary with Katharine McPhee, also mentioned his disdain for appearing on The Real Housewives of Beverly Hills beginning in 2012.

"My wife at the time wanted to do the show," he said. "I didn't want to be the guy to say no."

Announcing their divorce in December 2015, Foster and Hadid told PEOPLE in a joint statement that they'd decided to "go our separate ways." The pair tied the knot in November 2011.

"We've shared nine beautiful and joyous years together. During that time we experienced love, friendship and the inevitable challenges that come with managing a marriage, careers, blended families and health issues," read the statement at the time.

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"We are grateful for the years we've spent together and believe wholeheartedly that we did our best," the couple's statement continued. "I hope that we can pave the road ahead of us with all we've learned and with the love and respect we will always have for one another."

Hadid, 56, is now dating boyfriend Joseph Jingoli, whom she said she said she is "very much in love with" when speaking with Bravo's The Daily Dish in May.

In a 2016 episode of RHOBH, Hadid explained that "divorce is almost like a death," adding that "if you stop making each other happy, then you shouldn’t be together." She said at the time: “It’s shocking. David was my life partner. My best friend. And I miss my best friend.”

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Detailing his new documentary, Foster recently told PEOPLE that the film gives a never-before-seen look at his life.

"I never have been one to expose the vulnerable side of me, and I don't really ever talk about what makes me tick or the ups and downs of my life — the good, the bad and the ugly," Foster said. "But to [director Barry Avrich's] credit, he kept pushing."

"Although parts of it are tough for me to watch, I knew trying to censor him would be wrong on every level," he added. "So, I put my trust and faith in him, uncomfortable at times, but I have no regrets."

For more from David Foster and his daughters, pick up this week's issue of PEOPLE, on newsstands Friday.